1. Field of the Invention
The present invention relates to an image-capturing apparatus such as a digital camera. More specifically, the invention relates to an image-capturing apparatus having a camera shake correcting function, an image processing method applied to the image-capturing apparatus, and a program used in the image-capturing apparatus.
2. Description of the Related Art
There has recently been proposed a method of forming a low-noise, clear image without any blur in digital cameras. Such an image can be formed by performing a continuous shoot in short exposure time instead of one shoot in long exposure time and then superposing a plurality of images obtained by the continuous shoot.
Even though the time interval between frames in the continuous shoot is short, there is possibility that a displacement will be caused between a camera and a subject during the time interval. In order to superpose the images, the displacement has to be corrected.
As a conventional method of detecting a displacement between images due to a camera shake, Jpn. Pat. Appln. KOKAI Publication No. 10-173992 discloses a method of detecting a displacement between two images, which are picked up with a time difference, by correlating the images.
When a strobe light cannot be used, or when a subject is located away from a camera such that it is not sufficiently reached by the flash of a strobe light, an image is picked up at low light level and its SN ratio is very low. The feature of the subject is therefore difficult to extract. Consequently, there occurs a problem that a displacement between images due to a camera shake cannot be detected correctly or any images cannot be superposed satisfactorily.